The rigorous selection of ground motions is an important consideration in a seismic risk assessment as it provides the link between seismic hazard (seismology) and seismic response (earthquake engineering). Despite the fact that many studies have highlighted the differences between the uniform hazard spectrum (UHS) and individual earthquake scenarios, the UHS is still the primary method by which ground motion records are selected and scaled. The conditional mean spectrum (CMS) is one alternative to the UHS for ground motion selection which provides the mean response spectral ordinates conditioned on the occurrence of a specific value of a single spectral period, and is directly linked to probabilistic seismic hazard analysis (PSHA). There are however several limitations in the use of the CMS for ground motion selection, which primarily stem from the fact that spectral accelerations provide only a partial picture of the true character of a ground motion.Based on the identified limitations of the CMS the objective of this work was to develop what is referred to as a generalised conditional intensity measure (GCIM) approach, which allows for the construction of the conditional distribution of any ground motion intensity measure. A holistic method of ground motion selection was also developed based on the comparison of the empirical distribution of a ground motion suite and the GCIM distributions. Background and Objective Bias in Seismic Response from Incompatible Ground Motions Holistic Ground Motion SelectionIf a ground motion suite is selected which is not consistent with the GCIM distribution for a particular intensity measure, then there is possibly bias in the seismic response analysis if it is dependent on this intensity measure. The bias can be simply estimated using the dependence of the seismic response distribution and determine whether a new suite of (more representative) ground motions should be selected. ReferencesBradley, B.A. (2010) A Generalised Conditional Intensity Measure Approach and Holistic Ground Motion Selection. Earthquake Engineering and Structural Dynamics (in press -available online or from the author via email)The fundamental basis of the GCIM approach is that for a given earthquake scenario (Rup) the joint distribution of a vector of intensity measures (i.e. IM|Rup) has a multivariate lognormal distribution. The validity of this assumption and mathematical details are elaborated upon in Bradley (2010). Characterisation of IM|Rup, therefore requires the marginal distributions, IM i |Rup and correlations between IM i and IM j for which several prediction equations already exist. The total probability theorem can then be used to construct the conditional distribution of any intensity measure given the occurrence of a specific value of another intensity measure. The figure below illustrates the seismic hazard disaggregation for Christchurch, New Zealand, for onesecond spectral acceleration, Sa(1.0), which has an annual exceedance probability of 1/475; as well as the conditional spectral ac...

A team of earthquake geologists, seismologists, and engineering seismologists has collectively produced an update of the national probabilistic seismic hazard (PSH) model for New Zealand (National Seismic Hazard Model, or NSHM). The new NSHM supersedes the earlier NSHM published in 2002 and used as the hazard basis for the New Zealand Loadings Standard and numerous other end-user applications. The new NSHM incorporates a fault source model that has been updated with over 200 new onshore and offshore fault sources and utilizes new New Zealand-based and international scaling relationships for the parameterization of the faults. The distributed seismicity model has also been updated to include post-1997 seismicity data, a new seismicity regionalization, and improved methodology for calculation of the seismicity parameters. Probabilistic seismic hazard maps produced from the new NSHM show a similar pattern of hazard to the earlier model at the national scale, but there are some significant reductions and increases in hazard at the regional scale. The national-scale differences between the new and earlier NSHM appear less than those seen between much earlier national models, indicating that some degree of consistency has been achieved in the national-scale pattern of hazard estimates, at least for return periods of 475 years and greater.Online Material: Table of fault source parameters for the 2010 national seismichazard model.

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